Roller bearing
Theoretical information on roller bearings
Palmgren A. Ball and roller bearing engineering //Philadelphia: SKF Industries Inc. – 1959. – Т. 1.

where:
z is the number of rolling elements;
L is the roller length;
P is the radial load;
α is the contact angle.
Ball bearing
Theoretical information on ball bearings
Gargiulo E. P. A simple way to estimate bearing stiffness //Machine Design. – 1980. – Т. 52. – №. 17. – С. 107-110.

where:
z is the number of rolling elements;
D is the ball diameter;
P is the radial load;
α is the contact angle.